<<!DOCTYPE html>
    <html>

    <head>
        <meta charset="utf-8" />
        <meta http-equiv="X-UA-Compatible" content="IE=edge">
        <title>Page Title</title>
        <meta name="viewport" content="width=device-width, initial-scale=1">
        <script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>

    </head>
    <div id="app">
        <p>{{ foo }}</p>
        <!-- 这里的 `foo` 不会更新！ -->
        <button v-on:click="foo = 'baz'">Change it</button>
    </div>
    <hr>
    <div id="example"></div>

    <body>
        <script src="demo1.js"></script>
        <script src="demo2.js"></script>
        <script src="demo3.js"></script>
        <script src="demo4.js"></script>

    </body>

    </html>